The video that surfaced this week of four Marines apparently urinating on three Taliban corpses has stirred outrage in the U.S. and beyond, but also focused attention on the brutalizing effects of war on those sent to wage it.

Reserve Marine Lt. Col. Paul Hackett, who teaches the law of war to Marines before they are sent off to Afghanistan, made it clear Friday that he was not condoning the Marines’ actions. But he warned against judging them too harshly, saying: “When you ask young men to go kill people for a living, it takes a whole lot of effort to rein that in.”

In the long history of war, the episode pales in comparison to other battlefield atrocities. But one difference this time was that, in the Internet age, it was captured on camera and instantly shared with the rest of the world.

“This outrage is so interesting to me because it almost tops that” of other, more ghastly war crimes, said psychologist Eric Zillmer, a Drexel University professor and co-editor of the book “Military Psychology: Clinical and Operational Applications.” “Because of the technology, the video, you actually see it. Most of the other war crimes, you heard about, you read about.”

The Geneva Conventions forbid the desecration of the dead, and officials in the U.S. and abroad have called for swift punishment for the four Marines, identified as members of the 3rd Battalion, 2nd Marines, which fought in the Afghan province of Helmand for seven months before returning to Camp Lejeune, N.C.

The prohibition against desecrating the battlefield dead is almost as old as war itself.

In Homer’s “Iliad,” the epic poem about the Trojan War, which may have occurred in the 12th century B.C., Achilles kills Hector and refuses to allow for a proper burial. He relents after Zeus sends word that Achilles “tempts the wrath of heaven too far” with his desire to “vent his mad vengeance on the sacred dead.”

In the 7th century, Abu Bakr, father-in-law of the prophet Muhammad and Islam’s first caliph, issued 10 rules to his people for their guidance on the battlefield. Among them: “You must not mutilate dead bodies.”

In 1907, the Hague Convention said that after every engagement, the combatants should take steps to protect the dead against “pillage.” The first Geneva Convention in 1949 addressed preventing the dead from “being despoiled.”

The history of war is replete with stories of atrocities committed to send a message. In the 15th century, Prince Vlad III of Wallachia struck fear in his Turkish enemies – and earned his gruesome nickname, Vlad the Impaler – by littering the battlefield with the impaled corpses of the vanquished.

Over the centuries, fingers, scalps and other body parts have been taken as battlefield trophies.

Nevertheless, Zillmer said the desecration of a dead foe is “taboo across cultures.”

“It doesn’t need to be explained to be inappropriate,” he said. “Anybody who looks at it says it’s disgusting.”

But, like Hackett, he said it can be difficult for soldiers, particularly members of a tightknit group, to go on killing missions and then just “switch off.” And he said the inhibitions against such misconduct tend to fall away as the number of participants increases, a phenomenon he calls “diffusion of responsibility.”

Soldiers have long understood that savagery begets savagery – or at least breeds indifference.

In his World War II memoir “With the Old Breed,” E.B. Sledge wrote of seeing the bloated, blackened corpse of a fellow Marine on the Pacific island of Peleliu, his head and hands cut off, his severed penis stuffed in his mouth.

“My emotions solidified into rage and a hatred for the Japanese beyond anything I ever had experienced,” he wrote. “From that moment on I never felt the least pity or compassion for them no matter what the circumstances. My comrades would field-strip their packs and pockets for souvenirs and take gold teeth, but I never saw a Marine commit the kind of barbaric mutilation the Japanese committed if they had access to our dead.”

Urinating on the dead is not exactly a new idea.

In the same book, Sledge wrote with disgust about a young Marine officer on Okinawa: “If he could, that `gentleman by the act of Congress’ would locate a Japanese corpse, stand over it, and urinate in its mouth. It was the most repulsive thing I ever saw an American do in the war. I was ashamed that he was a Marine officer.”

On the very day the video from Afghanistan emerged, Sgt. Sanick Dela Cruz took the stand in a courtroom at Camp Pendleton in California and testified that he urinated on the skull of a dead Iraqi in 2005. Dela Cruz made the admission during the court-martial of a Marine charged in the killings of 24 Iraqis in the town of Haditha.

Dela Cruz said he was overcome with grief over a comrade killed by a roadside bomb. “The emotion took over, sir,” he told a military defense attorney.

Marty Brenner, an anger management specialist in Beverly Hills, Calif., who treats combat veterans and civilians, said the acts depicted in the video – and the Marines’ recording of it – demonstrate rage.

“They have no other way of expressing their anger at these people,” Brenner said, “so what they’re doing is urinating on them to show, `I’m better. I want the world to see you guys are crap and that’s what you deserve.'”

In Jacksonville, N.C., the home of Camp Lejeune, some people resented criticism of the Marines over the video, and some expressed fear the footage would make their job harder.

“It demolished me to see that,” said Arthur Wade, a Vietnam veteran who retired in 1989. “If one of those men being urinated on was your father, would you want to help the United States?”

But Maynard Sinclair, a Marine veteran of Vietnam and the peacekeeping mission in Beirut, said the outrage shows the public’s naivete about war.

“I did a hell of a lot worse in Vietnam than urinate on some dead bodies,” he said. “We cut left ears off and wore them around our necks to show we were warriors, and we knew how to get revenge.”

Gary Solis, a former Marine Corps prosecutor and judge who teaches law of war at Georgetown University, said the Internet has added a dimension that soldiers in the past did not have to deal with: “In Vietnam, when you screwed up, no one back home heard about it.”